Active & Passive Transport in Cells

Active & Passive Transport in Cells
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  • 0:01 Swimming in Solutions
  • 0:43 Moving Cellular Material
  • 1:58 Passive Transport
  • 3:50 Active Transport
  • 5:02 Lesson Summary
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Lesson Transcript
Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

Every second of every day, your cells are restocked with vital nutrients while getting rid of waste products. How does all this go on, you ask? Find out in this lesson on active and passive transport in cells.

Swimming in Solutions

Let's pretend for a moment that you're on vacation at the Dead Sea. You've already done the mud wraps and seen the sights, so now you're getting ready to go float around a little while. You see that there is an obnoxious tour group down at the beach, so you decide to go to the pool instead.

After almost an hour of floating around, you notice that your fingers and toes have become wrinkled. However, you also notice that the tour group has left. You grab your newspaper and camera and head down to the beach. You take all the standard pictures of floating in the ultra salty water, but after 30 minutes or so you notice that your fingers and toes are no longer wrinkled. In fact, they are a little swollen. What in the world happened?

Moving Cellular Material

In short, you have just seen your hands and feet go through a process that happens billions of times across the human body. Surely you've heard the fact that the human body is more than 70% water. It is through this water that cells receive nutrients and get rid of wastes. So how do they do that?

In short, cells are able to move nutrients and waste products due to passive transport and active transport. Passive transport involves moving nutrients from a more highly concentrated solution to a lower concentrated solution without the use of energy. In other words, it just happens. Meanwhile, active transport involves moving material from a less concentrated solution to a more highly concentrated solution and uses energy.

Think about it like this. Imagine a party which is going on in your dorm room. Passive transport would involve your next door neighbor opening their door and inviting some of your guests to come over. There is more room, which means that the solution is now at a lower concentration. Assuming you don't have any weird friends that no one wants to be around, there will be roughly equally sized groups of people in each room. Meanwhile, active transport occurs when your neighbor changes his mind and decides that they need sleep. They push everyone into a smaller area, namely your dorm room.

Passive Transport

Passive transport, once again, involves going from a highly concentrated solution to a lower concentrated solution. In the body, there is a spectrum known as the concentration gradient that emerges. At one end of the spectrum, the most highly concentrated parts of the solution congregate. At the other end, the least likely concentrated parts exist. Think about pouring water on top of sand. It may puddle up at first, but eventually the water will be absorbed by the sand. It is far from instantaneous - just like your neighbor opening his door to your party, half of your guests will not randomly decide to leave. Instead, it takes time.

Also, sometimes there is a barrier in-between the two solutions that only let certain materials pass. This is known as being semi-permeable. In other words, it's like your door. The materials that you would prefer to have the ability to pass through the membrane can do so easily, namely people. However, if you had reconstructed a car in your room as a prank, you cannot suddenly move it from one room to the other.

There are three major ways that passive transport can occur. The first is simple diffusion, when dissolved materials slowly even out in concentration over time. This is the equivalent of someone saying that the room next door is open. Slowly, over time people will move over.

The second is called facilitated diffusion, when another forces help to facilitate the transfer of materials. Let's say your next-door neighbor had a crush on one of your guests. Facilitated diffusion would involve him asking her and her friends if they wanted to come hang out in his room.

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